A local-area network (LAN) is a computer network that spans a relatively small area or domain. Most LANs are confined to a single building or group of buildings. However, one LAN can be connected to other LANs over any distance often spanning an area greater than either LAN via telephone lines, coaxial cable, optical fiber, free-space optics and radio waves. A system of LANs can be connected in this way via other networks that are commonly referred to as wide-area networks (WANs).